Over the last decade permeable for water vapor and smoke melt-extrudable films based on synthetic resins mainly on polyamide resins, used as casings for smoked sausages and frankfurters were entered into a packaging market.
Single-layer smoke and water vapor permeable films based on polyamide resins such as poly-ε-caproamide (hereinafter referred to as PA6), copolymer of poly-ε-caproamide and poly hexamethylene adipamide (hereinafter referred to as PA6/66) and comprising 4 to 50 wt. % of hydrophilic compounds including water-soluble polymers such as polyvinylpyrrolidone (hereinafter referred to as PVP), polyvinyl alcohol (hereinafter referred to as PVA), that can form in polyamide matrix a highly dispersed phase with a linear size (thickness) of a domain of 0.1-3.0 μm (mcm), as well a method of making thereof was disclosed in patent RU No2182107, publ. 10 May 2002. They are characterized with relatively low cost (comparable with a level of conventional biaxially oriented polyamide film cost) and easy in production. Such films being used as sausage casings, allow preparing sausages, including frankfurters, having the pronounced features of smoking and a typical dense dark own skin (or a crust) on their surfaces.
Films, made of compositions with PVA as a hydrophilic compound are particularly easy in production and beneficial in point of in point of material cost. Such films were commercialized by Atlantis-Pak Ltd., as a product portfolio of smokable casings. Process of their improving led to recognition of the fact, that PVA content increasing results in growth of smoke- and water vapour permeabilities of these films, that is quite desirable in point of casing for smoked sausages performances. Meanwhile, mechanical strength of such casings decreases with the growth of PVA content. If it is more than 20%, such problems as bursts or breaks of these casings during their industrial high-performance and high-speed production as well in process of sausages and frankfurters stuffing into these casings often take place. And if casing additionally comprises such mechanically weak polymers, as, for instance, block-copolymers of polyamide and polyether, in a layer comprising PA and PVA, as disclosed in Patent RU No2333652, publ. 20 Sep. 2008, or in a layer not comprising PVA, above problems can arise even at lower PVA percentage.
Thus, the object of the present invention is a film, comprising (co)polyamide and PVA, particularly suitable for use as a casing for foods, but free of above drawback.